Method of structurally modifying the surfaces of metal bodies



O. E. ANDRUS July 12, 1932.

METHOD OF STRUCTURALLY MODIFYING THE SURFACES 0F METAL BODIES Sheets-Sheet l II!!!IllIllIlIlIIIIIIIIlIIIIlI/l I N VEN TOR.

A TTORNE Y.

July 12, 1932. R'U 1,866,538

union or smucruanu monxmua was suamcns 0F mam. aonms Filed July 1a. 1928 2 Sheets-Sheet 2 INVENTOR. ORR/IV E. Ana/90.9

ATTORNEY. 4

Patented July 12, 1932 UNITED (STATES PATENT OFFICE OBBIN E. ANDRUS, O1! MHJWAUKEE, WISCONSIN, ASSIGNOR TO A. 0. SMITH CORPORA- TION, OF MILWAUKEE, WISCONSIN, A CORPORATION OI NEW YORK METHOD OI STBUOTUBALLY MODIFYING THE SURFACES OI METAL BODIES Application filed July 13,

M invention relates'to a method of structura 1y modifying a surface of a metal'body by applying thereto an electric current havin suflicient intensity to raise the temperature 5 a portion of said metal body above transformation temperature by reason of the natural resistance of the metal of said body to the flow of the said electric current.

Some ofthe various purposes for which the invention is suitable may be stated as follows: (a) to surface harden high carbon steel; (b) to surface harden carburized steel; (0) to surface toughen low carbon steel; and (d to surface harden cast iron.

eretofore, the surfaces of metal bodies have been structurallymodified in a number of different manners, but usually by subjecting the bodies to a high temperature, as, for example, in a furnace, to raise the temiio perature of the whole of their surfaces above transformation, temperature, and then quenching the bodies. Such procedure, obviously, changes the entire structure of the bodies and has tendency toward developing stresses and warping in the bodies. To'obviate stresses and warping and changes in the entire structure, attempts have been made tostructurally modify the surfaces of metal bodies by the external application of localized heat to the said surfaces. aware, satisfactory structural modification of thesurfaces of metal bodies has not been attained by the external application to the surfaces of localized heat, for the reason that all attemptsto make the methods continuous, by 'the external application of localized heat to portions of a surface adjacent portions already modified by externally applied localized heat, have either resulted in further modification, of a substantial part at least, of thesaid already modified portions, so that the surfaces have been of greatly varied structure throughout their areas, and not of a substantially uniform and predetermined modified structure, or have resulted in the melting or burning of the surface because of a too intense localized heat. 1

.By way of example, it may be said that should it be desired to acquire a modified sur- 50 face of a uniform and predetermined struc- But, so far as I am' 1928. serial no. 292,377.

ture upon a carbon steel, such as would result from heating the whole of the surface of the steel to critical temperature and quick-' 1y quenching, there would be a failure in the attemptsto accomplish this result by repeatedexternal applications of localized heat,

rially heated. The external application of' localized heat to a surface of a metal body, as, for example, carbon steel, to raise a portion thereof above transformation temperature, and without melting or burning the metal, of necessity causes a considerable spreading of the heat to surrounding areas of the surface, so that portions of the metal dlrectly surrounding portions raised above transformation temperature are just belowtransformatlon temperature, while surround-.

ing portions further removed are but little cooler. In fact, a surrounding area of considerable dimensions is materially heated when a portion of a metal surface is raised above transformation temperature by the external application of localized heat, andthe temperature of the said surrounding. area varies about uniformly from the perimeter of the area above transformation temperature, where said surrounding area is hottest, to a perimeter remote from the transformation temperature area. where said surrounding area is coolest. Thus, as will be evident, when a repeated external application of localized heat is made upon a portion of the surface of a metal body adjacent a portion thereof already heat treated, there is considerable heat lap-overwhich results in material alteration of the structure of practically all, if not all,.of the said portion already heat treated, and the structure of the already treated portion is affected, to an ever varying degree, practically throughout its whole area. Y

An object of the present invention is the .provision of a method for structurally mod- 8 1fying a surface of a metal body by applying thereto anelectric current adapted to raise substantially instantaneously the temperature of a portion of the surface of said .metal body above transformation temperature, by reasonof the natural resistance of the metal of .said body to the flow of the current, with-' out materiall heatin other portions of said surface whic are adjacent the said portion raised above transformation temperature, 16 whereby applications of localized heat to different and contiguous portions of the said surface can suflice to produce upon said metal body a modified surface of practically uniform and predetermined structure.

90 A further object is the rovision of a method for structurally modi ying a surface of a. metal bod by applying thereto an electric current a apted to locally and ractically instantaneously heat a portion of t e surface, and a localized region of said metal body contiguous with the heated portion of the surface and substantially surrounded by unheated metal of said body, above the-transformation temperature of the metal, in such man- .'ner that the heat applied to the said surface and localized re 'on will not spread to any material extent, at will be concentrated substantially within the said localized heated region, whereby unheated metal of the said body surroundmg the said localized heated region can materially assist in the quenching operation.

A further object is the provision of a method as stated, wherein the application of the localized heat to the surface of a metal body is accomplished by the utilization of one or more resistance heating electrodes, and in such manner that the portion of the surface heated above transformation temperature is engaged by a resistance heating electrode while the localized heated region situated within and is substantially surrounded by the mass of the unheated metal of the body.

A still further object is theprovision of a method as stated, wherein the practically instantaneous application of the localized heat to the surface of a metal body is accomplished by causing a resistance heating electrode to,

but momentarily enga e each portion of the raise the temperature of the said portion above the transformation temperature of the metal, whereby the concentrated action of the current can be applied to a portion of the said surface and in overlapping relation to a contiguous portion already modified without altering the structure of the said already modified portion.

And another object is the provision of a 53 method as stated, where n the resistance heatmeshes with a worm wheel 16 having a hub 17 upon the outer end of said short shaft is for said surface to practically instantaneously ing electrodes utilized are referably, but not necessarily, roller electrod es adapted to ride over the surface of the body of metal. With'the above objects in view, as well as others which will appear as the specification proceeds, the invention will now be fully described and will hereinafter be specifically clatimedl.

n t e accompan in drawin formin a part of this speciliha on, gs g Fig. 1 is an elevational view, partially sectioned of an apparatus by. utilization of which the improved method can be practiced, the disclosure also including a metal cylinder, having a surface to be hardened, as when acted upon by the apparatus; Fi 2 is a sectional view taken as on line 22 1n Fig. 1;

Fig. 3 is an elevational view, partially sectioned, of a modified type of apparatus for practicing the novel method, the disclosure also including a metal rail, having a surface to be hardened, as when acted upon by the modified apparatus; and

Fig. 4 is a sectional view taken as on line 44 in Fig. 3.

With respect to Figs. 1 and 2 of the drawings, A represents a metal cylinder having an external surface B which is to be structurally modified. The cylinder A may be composed of any one of a variety of different metals. For example, it may be high carbon steel, carburized steel, low carbon steel, or cast iron.

As disclosed, the cylinder A is situated in cooling .liquid C of any suitable nature contained in a vessel 10, and the said cylinder is rotatably supported in the vessel, in spaced relation to its walls, bymeans of studs 11 upon the cylinder which rest upon rollers 12 conveniently mounted in brackets 13 sup- 105 ported upon thebase of the vessel.

Any suitable mechanism may be utilized to rotate the cylinder. As shown, a worm 14 supported by a bracket 15 upon thevessel no mounted in a bifurcated part 18 of said bracket 15, as at 19, and. a short shaft 20 splined to the hub has an hexagonal end portion 21 adapted to fit an hexagonal opening 22 in a plate 23 secured as at24 to the adjacent stud 11 upon the cylinder. The short shaft 20 is slidably situated in a gland 25 of the adjacent wall of'the vessel, afid a hand piece 26 the purpose of manipulating the hexagonal 139 end portion 21 into and out of the opening 22 of the plate 23. Clearly, when the hexagonal end portion 21 of the short shaft 20 is situated within the opening of the plate 23, turning o the worm 14 will cause the cylinder A to be rotated upon its bearings, or the cylinder can be rotated by turning the hand piece 26.

A double track 27, above and parallel with the vessel 10, supports wheels 28 mountedv upon a source of electric current supply, rep- 1:0.

" any suitable manner. As disclosed, verticall disposed rods31, extending downwardly rom said element 29, have their lower portions threaded, as at 32, and transverse plates 33 are supported upon the threaded portions of said rods, in spaced relation to each other by nuts 34 upon the rods above and below the plates and spacing sleeves 35 upon the rods and between the plates. Roller electrode carrying shanks 36, of conducting material, have bifurcated lower portions 37 in which the roller electrodes 30 are mounted, and the up per portions of the said shanks 36 -are slidable in insulation 38 in openings of the spaced apart plates 33. Coil springs 39 upon the shanks 36, bearing attheir upper ends against the insulation in the upper plate 33 andat their lower ends against. collars 40 upon the shanks, yieldingly urge the roller electrodes 30 toward the cylinder A, and nuts 41 u on the said shanks 36 and above the upper p ate 33 limit the extent of downward movement of the roller electrodes, as will be obvious.

Numeral 42 represents leads from the source of electric current supply, or transformer 29, to the electrodes. As shown, the

lower ends of the leads 42 include eyes 43 of conducting material snugly engaging the shanks 36.

As clearly disclosed in Fig. 2, cooling liquid supply pipes 44 may deliver cooling liquid to the vessel at the locations of the roller electrodes, and an overflow pipe 45 may lead from the upper part of the vessel.

With respect to Figsi 3 and 4 of the drawings, I have there shown a metal rail A having surfaces B to be structurally modified. The rail may likewise be composed of any one of 'a variety of difierent metals.

As disclosed, the rail A is suitably suspended from a pulley 46 and is adapted to be lowered into cooling liquid C in a suitable vcssellO', and past roller electrodes 30' which yieldinglyengage opposed faces of the said (not shown), snugly engage the shanks 36.

Numerals 44' and 45 represent, respectively, cooling liquid supply and overflow pipes, as before described.

Numeral 47 represents guide rolls for the rail suitably mounted in opposed relation upon the walls of the vessel adjacent the walls which support the roller electrodes.

While in each instance I have disclosed the workingportions of the roller electrodes submerged in ,the cooling liquid, it is to be understood that the operation may be carried out in the atmosphere, although it is preferable to have the body being heat treated at least partially submerged in a cooling liquid. or a cooling liquid may be sprayed upon the body at the location of the electrodes.

I have preferred to disclose resistance heating electrodes of the roller type, but in certain instances spot electrodes, or even sliding or wiping electrodes, may desirably be employed.

In the instance of either form of my improved apparatusas disclosed, the roller electrodes and the surface being heat treated are given movement relatively to each other and the electrodes are caused to roll over the surface while current'is caused to flow through heat applied to the said surface and localized region will not spread to any material extent, but will be concentrated substantially within the localized heated region, and the resistance heating of the surface will be so accomplished that unheated metal of the said body will surround the localized heated region to materially assist in the quenching operation. That is to say, I accomplish the resistance heating in such manner that the portion of the surface heated above trans-- formation temperature is engaged and protectedby a resistance heatin g electrode, while the localized region heated above transformation temperature and contiguous with the surface heated above transformation temperature isgsituated within the 'metal body beneath'the heated portion of the surface, and is substantially surrounded by the massof the unheated metal of the said body. This result is accomplished, as will be apparent, by the utilization of an electrodehaving a contactthe body to locally and practically instani ing area which is relatively small compared to the mass of the metal body being heat treated, and by controlling the depth into the interior of the metal body to which the localized heated region extends. The conditions can be varied by varying the intensity of the current, the sizeoftheelectrode contact, the time of application of the current, or the bulk.and--thicknss of the metal body. The

depth of the localized region heated above transformation temperature will preferably be less than a measurement representing the thickness of the metal-at position adjacent 5 the localized heated region so that there will be a bulk of practically unheated quenching metal substantially surrounding the said localized heated region. Considered from a different aspect, practically the whole of the whole of the localized heated region will be situated internally of the metal, beneath the locally heated portion of the surface there of,'.to be substantially surrounded by unheated quenchin metal of the bulk of metal. The reason w y exceedin ly satisfactory results in structurally modifying a surface of a. metal body by resistance heating can be obtained will be readily appreciated when it is realized that resistance heating applied by causing a relatively small electrode, usually a copper electrode, to engage a surface of larger area does not cause the heat to be wholly external. .On the contrary, the highest temperature attained is beneath the surface, not far distant therefrom, and ina plane substantially arallelwith'the engaging face of the electr e. As a consequence, the heating of a portion of the metal at and adjacent the surface above critical temperature is accomplished practically instantaneously. Immediatel the heated area is quenched, at least partia 1y by the unheated bulk of metal surroundin the heated area, so that there is no materia interval of time in which the heat can spread to portions of a surface adjacent a heat treated portion. Thus, evidently, ap lications of localized heat to different an contiguous ortions of a surface of a metal body, and s cing to produce upon said body a modified. surface of practically uniform and predetermined structure, can be accomplished.

.By the employment of electric resistance heating, a minimum amount of heat, considmetal body being heat treated and its capacity to-absorb heat, can be concentrated at and adjacent a surface of a metal body to ,raise the temperature of a localized region of said body above the transformation temperature ofthe metal without causi'n such a spread of the the heat to already mo 'fied adjacent areas of the surface as will materially alter the structure of the said adjacent areas. By reason of the fact that the concentrated heat can he so relativel small in amount com-' pared to the total bul of metal and its heat absorbing capacity, the arrangement can be such that the temperature of the whole body of metal can be caused to immediately drop below the tempering range practically instantaneously, and during a continuous. operation, the bulk of metal can continuously and swiftly absorb the small amount 'of heat which it is necessary to apply without causered from the standpoint of the bulk of a ing the temperature of the whole mass of' metal to be appreciably elevated as a result.

Naturally, the quenching liquid, or other medium, functions continuously to remove by overlapping spots about one-half inch in diameter upon the surface of a steel block. The heatin was, produced by a heavy current applie through a copper electrode. 1 have also used a roller electrode the axis of which was held stationary and the metal body moved relatively to it. Such an arrangement greatly increases the speed and ease of carrying out the surface modifying operation. With some t of work, as, for example,- the cylinder disclosed in Figs. 1 and 2, the method of heating by use of a roller electrode can be made automatic. The cylinder A can bemade to rotate at constant v while a slow constant movement of the electrodes longitudinally of the cylinder is accomplishe to thus produce a continuous modified surface of practically uniform and predetermined structure upon the surface B of the cylinder.' The movement made by the electrodes over the surface B would, in such an event, desirably be along the line of a helical .band the edges of which overlapped.

When a resistance heating electrode. is utilized to modify a surface of a metal body by overlappingly'engaging contiguous portions of the said surface, the overlapped portions. are, obviously, heated more than once;

through the tempering range of the metal.

But by reason of the fact that the saideover lapped portions can be so quickly passed through the temperingrange, the structure thereof is not materially altered by-th'e 1 5- peated heating. v

While'I have, in the instance of each form of the apparatus; disclosed two resistance heating electrodes, it will be obvious that a single resistance heating electrode may in some instances be preferable.

The present method of structurally modifying the surfaces of metal bodiesisespeciall in my method is due to alarge extent to the fact that the metal body can itself materially assist in the quenching operations to thus hasten the quenching.

It should be noted that my novel method has no relation whatsoever to the heat treatment of the full thickness of a metal body, or-ofan element, as, for example, a saw tooth, protruding therefrom, by the single application thereto of a resistance heating electrode.

. On the contrary, the present method contemplates structurally modifying onl the surace of a metal body by separately eat treating a plurality ofdiiferent portions of the sand surface, each of which ortions is of less area than the whole area 0 the surface and is substantially surrounded by a considerable'bulk of quenching metal of the body.

Having thus fully described my invention, what I c aim and desire to secure by Letters Patent of the United States, is:

1. The method of structurally modifying a surface of a metal body by application thereto of an electric current having suflicient intensity to raise substantially instantaneously the temperature of a portion of said metal body above transformation temperature by reason of the natural resistance of the metal of said body to the How of the current, which consists in subjecting a portion of the surface to the concentrated action of said current, and causing the temperature of a localized region of said metal body conti uous with said portion of the surface an substantiall rounded on all of its sides, except its si e constituting the portion of the surfacesubjected to the current, by unheated metal of said body, to be raised above the transformation temperature of the metal, whereby the said unheated metal of the body about the said localized regionheated above transformation temperature can quickly absorb the applied heat at the expiration of the interval of its application. r a

2. The method of structurallymodifying a surface of a metal body by application thereto of an electric current having suflicient intensity to raise substantially instantaneouslythe temperature of a portion of said metal body above transformation temperature by reason of the natural resistance of the metal of said body to the flow of the current, which consists in sub'ecting a relatively small portion of the sur aceto the concentrated action of said current, caifsin the temperature of'a relatively small local ized region of .said metal body contiguous with said relatively small portion of the surface and substantially surrounded on all of its sides," except its side constituting the relatively small portion of the surface subjected to the current, by a relatively large, practically unheated bulk of metal of said body, to be raised above. thetransformation temperature of the metal,

whereby the said practically unheated, relatively large bulk of metal of said-body about ,the said relatively small localized region heated above transformation temperature can quicklyabsorb the ap lied heat at the expiration of the interval 0 its application to cause the temperature of the whole body-of metal to fall below the tempering range of the metal, and cooling said metal body.

3. The method of structurally modifying a surface of a metal body by application thereto of an electric current having sufficient intensity to raise substantially instantaneously the temperature of a portionof said metal body above transformation temperature by reason of the natural resistance of the metal of said body to the flow of the current, which consists in subjecting a portion of the surface of the metal body by surrounding the same with a cooling medium.

4. The method of structurally modifying a surface of a metal body by application thereto of an electric current having sufiicient intensity to raise the temperature of a portion of said metal body above transforma tion temperature by reason of the natural resistance of the metal of said body to the flow of the current, which consists in sub'ecting contiguous portions of the surface to t (9 concentrated action of said current applied in overlapping relation to the said contiguous ortions, and thereby causing a modified surace of practically uniform and-predetere metal body. 7

'5. The method of structurally modifying a surface of a metal body by application thereto of an electric current having sufiicient intensity to raise substantially instantaneously the temperature of a portion of said metal body above transformation tempera ture by reason of the natural resistance of the metal of said body to the flow of the current, which consists in successively subjecting contiguous overlapping portions of the surface to the concentrated action of said current to thereby produce a modified surface ,of practically uniform and predeter mined structure upon said metal bod 6. The method of structurally modifying a surface of a cylindrical metal body by ap:

plication thereto of an electric current hav- ,mined'structure to be produced upon said I of said cylindrical metal'body above transformation temperature by reason of the natural resistance of the metal of said body to the flow of the current,-which consists in rotating the cylindrical body and subjecting successive contiguous portions of the surface thereof to the concentratedaction of said current to thereby produce a modified surface of practically uniform and predeter- 11386. structure upon said cylindrical metal 4 7. The method of heat treating the con- -tinuous surface portion of a metal body 10 which comprises bringing a movable electrode of limited contact surface into pressure. contact with a portion of the surface to be treated to thereby apply a concentrated electric current to the metal of the bod immediately beneath said electrode, an progressively moving said contacting electrode relative to said surface to successively heat contiguous surface portions of said bodyto the required temperature at a rate sufiizo cient to substantially prevent detrimental conduction of heat to surface portions already subjected to heat treatment.

8. The method of heat treating the continuous surface portion of a metal bod :5 which comprises ringing a roller electro e into contact with a portion of the surface to be treated, applying an electric current to said body through said electrode to heat a portion of said body immediatel beneath the $0 limited contact of said electro e for a substantial depth to the required temperature for heat treating the same, and relatively rotating said contacting electrode along the surface to. be treated to progressively and successively heat treat contiguous surface portions of said body to the required depth at a rate suflicient to prevent detrimental conduction of heat to surface portions previously subjected to heat treatment. 40 In testimony whereof, I have signed my name at Milwaukee, this 11th day of July,

ORRIN E. ANDRUS. 

